Redmine #6171: Improve acceptance test speed on Windows.

Run the entire test suite under one single GAINROOT umbrella, instead
of launching it for each test. This dramatically improves the testing
speed on Windows.
... except that echo $1 reduced each block of spaces to a single space !
```
echo one                        two | wc
echo one two | wc
```
produce identical results.
You need `echo "$1"` but I'm not sure how that works with the outer "..." around the whole mess.